In modern glass container manufacturing practice, most containers are manufactured on an I.S. machine. An I.S. machine has a multiplicity of side-by-side container forming sections, typically six, eight, ten or even twelve sections, and containers are formed at each such section from gobs of molten glass in two steps. In the first step, a preform of each container, which is often referred to as a blank or a parison, is formed by blowing or pressing, in an inverted position, that is, with the open end of the preform below its closed end. The closure receiving portion of the container at its open end is molded by a neck mold assembly, which is often referred to as a neck ring assembly and is made up of a separable pair of neck ring elements, and the body portion of the preform is formed by a mold assembly, which is made up of a separable pair of mold elements that, when closed, collectively define an internal cavity with a shape corresponding to the desired shape of the preform.
After completion of the blank forming step, the blank and usually two, three or even four like blanks made simultaneously at each machine section, is transferred by a 180.degree. inverting operation to a second position where each preform is blown into the desired final shape of a container within the cavity defined by the separable pair of mold elements.
The transfer of the preform from the blank molding station to the blow molding station is by way of an invert arm assembly. The invert arm assembly is made up of a side-by-side pair of invert arm sections that oscillate in unison to transfer the neck ring assemblies between the blank mold station and the blow mold station, the transfer from the blank mold station to the blow mold station being effective to transfer the blanks carried by the neck ring assemblies from the blank mold station to the blow mold station. The invert arm sections are capable of separating from one another at the blow mold station to permit the neck ring elements in the neck ring assemblies carried thereby to separate from one another, to thereby permit the blanks to be removed from the neck ring assemblies at the start of the blow molding step. The invert arm assembly sections are then brought back together as the invert arm assembly is returned to the blank molding station to begin a repeat of the cycle.
The oscillating motion of each invert arm assembly is usually actuated by a pneumatic cylinder that drives a rack in a rectilinear pattern, and a gear carried by a shaft to which the invert arm assembly sections are secured engages the rack, which leads to arcuate motion of the shaft as a result of rectilinear motion of the rack. The drive for an invert arm assembly in an I.S. glass container forming machine as thus far described is generally described in U.S. Pat. No. 3,617,233 (Mumford), the disclosure of which is incorporated by reference herein. Other U.S. Patents describing invert arm mechanisms include U.S. Pat. No. 3,445,218 (Trudeau), U.S. Pat. No. 3,573,027 (Nuzum, Sr.) and U.S. Pat. No. 3,233,999 (Mumford), the disclosure of each of which is also incorporated by reference herein.
The reversing motions of the invert arm assembly actuation cylinder and rack involve inertial loads of considerable magnitude at each end of the cycle of motion due to the considerable mass that must be rapidly decelerated at the conclusion of each motion, and these loads are especially high as the invert arm is moving from the blank molds to the blow molds because it is carrying glass container parisons during this motion. Because of this, it has been known to connect each cylinder, in parallel, to an elongate shock absorber so that the cessation of each motion will be precise and non-jarring. This is especially important in the case of a shock absorber that is used to cushion the deceleration of the invert arm assembly at the blow mold station, because glass container parisons are being carried by the invert arm assembly at this time and are subject to distortion under unduly high inertial loads. In any case, the useful life of each such shock absorber is somewhat limited, due to the breakage and/or wear it experiences as a result of the magnitude and frequency of the shock loads to which it is exposed during the normal operation of an I.S. machine, thus requiring frequent removal of such shock absorbers for repair or replacement. Heretofore, the removal and reassembly of an I.S. machine invert arm assembly invert motion shock absorber was a time-consuming procedure because it required the removal of the entire invert arm mechanism including the disconnecting and later reconnecting of the hydraulic lines leading thereto, and because of the limited working space available to maintenance personnel involved in such procedure. A time period of the order of 4-6 hours was typically required for such procedure and, of course, no glass containers could be produced at a machine section during this time. The procedure was also somewhat unpleasant to perform because of the elevated temperatures and the noise inherently present in the environment of an operating I.S. machine.